Transfusion therapy in the past was largely dependent on the use of whole blood. While whole blood may still be used in certain limited circumstances, the modern transfusion therapy depends largely on the use of the clinically needed blood component. Whole blood consists of many components, primarily, red blood cells, white blood cells, platelets, and plasma. Therefore, there was the need for specialized equipment capable of processing drawn blood from a donor to extract the needed component and return the rest back to the donor. These equipment, known as Apheresis equipment, are largely dependent on centrifugation processes to separate blood components. These centrifugation processes are divided in two categories, continuous flow process, and batch process.
Systems utilizing continuous flow process direct the flow of the whole blood drawn from a donor through one channel into a spinning centrifuge rotor where the components are separated. The needed component is collected and the unwanted components are returned to the donor through a second channel on a continuous basis as more whole blood is being drawn. The continuous flow has the advantage of having a low extracorporeal volume, since the blood is processed as it flows continuously from the donor through the system and back to the donor. The amount of blood that is out of the donor at any time during the procedure is relatively small. The disadvantage with this system is that although the processing chamber where the blood is separated has a small volume, it has a relatively large diameter and more often it has a large tube rotating around it at a larger radius. Consequently, the continuous systems are large and are complicated to set up and use. A major disadvantage to most continuous systems is that two separate channels are used simultaneously to drive blood from the donor and to return unwanted components back to the donor. In most applications the donor is punctured with two intravenous needles to secure the channels. These devices are used almost exclusively for the collection of platelets in blood bank environment. These devices are not used for blood washing and salvaging in the operating room (OR) environment, due to the large size and noise level.
Systems utilizing batch process draw whole blood from a donor and direct it through a channel to fill a spinning rotor with a constant volume. This type of rotors is intentionally built with relatively large volume to process a substantially large amount of blood at each batch cycle. When the rotor is full, the drawing of the blood from the donor is stopped. The unwanted components of the separated blood are returned to the donor through the same channel that used to draw blood. After returning unwanted components and the rotor is emptied, blood is drawn from the donor to start the second batch cycle. This process is repeated until the desired blood volume is processed or the desired component volume is collected. Systems with batch process are relatively small and more compact in size. The size of the rotor is very critical for the batch process. Large rotors speed up the process but require large extracorporeal volume. Small rotors slow down the process and require many batch cycles to collect one unit of needed component.
There have been many attempts to develop a batch process rotor with adjustable volume to accommodate for the variation of the processed batches of blood. The invention documented in U.S. Pat. Nos. 5,733,253, 6,074,335, and 6,099,491 describes a compact rotor comprising a rigid member and a flexible diaphragm. The diaphragm is stretched by vacuum to fill the rotor with blood then compressed by pressurized air to express the separated components. The fine thickness of the membrane and the inconsistency in stretching geometry mixed with the induced stresses generated by the centrifugal forces can cause the diaphragm to rupture catastrophically spilling out all the blood.
The whole body of the rotor in U.S. Pat. No. 3,737,096 is made of flexible PVC film. The volume of this rotor can vary to control the hematocrit of the final product. But the shape and the big size of the rotor necessitate the system to be large and awkward to handle.
There exists the need, therefore, for a centrifugal system for processing blood and other biological fluids that is compact, easy to use, and has a durable rotor capable of adjusting its volume.